WebKit is the engine that turns HTML, CSS, and JavaScript into the pages you see. The project describes itself plainly on its home page as “a fast, open source web browser engine,” and notes that it powers Safari, Mail, the App Store, and other applications across macOS, iOS, and Linux.
WebKit did not start from scratch. Apple began it as a fork of KHTML, the rendering component of the KDE desktop project’s Konqueror browser. The technical lineage is visible even in the software’s own identity string, which reads “AppleWebKit (KHTML, like Gecko),” a nod to its KHTML roots. A talk hosted on the WebKit blog covers “the early history of KHTML, as well as some of the newer things going on with WebKit and KHTML.”
On 7 June 2005, Apple opened up the full WebKit project. Where previously only the WebCore and JavaScriptCore components had been available as source, Apple now opened the entire engine along with its revision-control tree and bug tracker, making WebKit a fully open development effort.
For years WebKit was also the engine inside Google’s Chrome. In 2013 Google forked WebKit to create its own engine, Blink, but the two share a common ancestor in WebKit and, through it, in KHTML.